1. Field of the Invention
The present invention relates to a new variety of Drechslera monoceras, said variety showing no pathogenicity against crops but exhibiting pathogenicity against barnyard grass, weed control compositions containing the same as an effective ingredient and also weed control methods using the same.
2. Description of the Related Art
Serious problems have arisen in last several years from the excessive use of synthesized organic agricultural chemicals, including environmental pollution and reduced effects of control due to the occurrence of diseases, pests and weeds with acquired chemical resistance. Influence of agricultural chemicals to the human body and the natural environment is now increasingly reported to large extents by mass media. Further, the interests in biological control of pests have increased so that a great deal of research and development work is under way with respect to bioinsecticides and bioherbicides. Pesticideless or herbicideless cultivation methods and biological control methods are still in the middle of investigation. As a matter of fact, when applied singly, they cannot provide stable control effects so that no sufficient production of crops can be expected. Whatever control method is used, it is very significant from the viewpoint of safety to lower the dosage of a synthetic organic agricultural chemical.
In the field of herbicides, research and development work has been carried out, centered in the United States, with respect to bioherbicides which use a pathogen against weeds. Bioherbicides which have been put on the market to date include "DeVine" (trade mark; product of Abbott Laboratories Ltd.) and "Collego" (trade mark; product of Ecogen Inc.). The former makes use of Phytophthora palmivola which is a pathogen against strangle vine (Morrenia odorata), an Asclepiadaceae weed, while the latter utilizes Colletotrichum Eloeosporioides which is a pathogen against northern jointvetch (Aeschynomene virginica), a leguminous weed. To the best of the present inventors knowledge, no bioherbicide has been put into practical use against barnyard grass (Echinochloa spp.) which is a troublesome weed in the cultivation of important crops such as wheat, rice and soybean.
Wild species of barnyard grass are known as weeds in the rice crop areas of the world. Barnyard grass has long been a problem as a typical lowland weed especially in Japan. Occurrence of barnyard grass in paddy fields is said to have led to the need for transplanting of rice seedlings. According to Yabuno ["Zasso Kenkyu (Weed Research), Japan" 20 (1975)], barnyard grass which grows wild in the world includes Echinochloa oryzicola, Echinochloa colona, Echinochloa pyramidalis, Echinochloa stagnina, Echinochloa haplocloda and Echinochloa crus-galli, and the crus-galli species is classified into three varieties, namely, Echinochloa crus-galli var. formosensis, Echinochloa crus-galli var. crus-galli, Echinochloa crus-galli var. praticola. Among these varieties, different reactions are observed to herbicides and pathogens. Barnyard grass which grows naturally as a weed is considered to include hybrids of these Echinochloa species. As a herbicide having practical control effects against barnyard grass, it is therefore desired to have herbicidal effects against all the species of Echinochloa spp.. Even if herbicidal effects may not be exhibited against all the species of Echinochloa spp., it is required to have a broad herbicidal spectrum against at least practically troublesome species of Echinochloa spp..
When the surrounding temperature exceeds 10.degree. C., weed of Echinochloa spp. is allowed to germinate and begins to grow. To achieve more effective control, it is preferred to apply a herbicide at the same time as the time of germination of the weed of Echinochloa spp.. In Japanese lowlands, for example, the period of from May to June during which the water temperature arises to 10.degree.-15.degree. C. or so is the time for weed control.
It is therefore preferred for Echinochloa spp. control agents to have a broad herbicidal spectrum against the above-described various species of Echinochloa spp. and also to bring about good results even at a temperature as low as about 15.degree. C.
Reported as strains of Drechslera monoceras sp. collected from Echinochloa spp. include ATCC-24641 [American Type Culture Collection (ATCC) Catalogue of ATCC page 144] as well as IFO-9619 and IFO-9800 [Institute for Fermentation OSAKA (IFO) List of Culture page 177]. As will be described subsequently herein, these strains do not show any herbicidal activities against Echinochloa spp. and their esterase zymograms are different from those of the new variety according to the present invention.
Further, as Drechslera monoceras sp. capable of showing pathogenicity against Echinochloa spp., European Patent Applications Nos. 0464410A2 and 0374499-A1 disclose eleven (11) strains including MH-9011 (Ferm BP3416) as the most effective strain at 25.degree. C. These strains, as will be described subsequently herein, are also different in esterase zymogram from the new variety according to the present invention and show practically no herbicidal activities at the germination temperature of Echinochloa spp., that is, around 15.degree. C.
To achieve more effective control of Echinochloa spp. by a bioherbicide, there is an outstanding demand for the provision of a microorganism which has sufficient Echinochloa spp. control effects at temperatures as low as 15.degree. C. or so.
Besides barnyard grass, many weeds grow competitively with crops in lowlands and uplands. Control of these weeds is also essential in practice. To control these many weeds at once, it is the current common practice to use a few types of chemical herbicides in combination. Application of a variety of chemical herbicides in large amounts is however not preferred because as described above, it may result in the occurrence of weeds and insects with acquired herbicide resistance and also in the development of the problem of environmental contamination.